The present invention relates to hydrotalcite-based compound particles, a resin stabilizer using the particles, a halogen-containing resin composition and an anion scavenger using the particles. More particularly, the present invention relates to hydrotalcite-based compound particles having excellent effects of imparting a good thermal stability to resins and preventing initial coloration of the resins when added thereto, a resin stabilizer using the hydrotalcite-based compound particles, a halogen-containing resin composition containing hydrotalcite-based compound particles, and an anion scavenger using the hydrotalcite-based compound particles.
The hydrotalcite-based compound particles of the present invention are capable of capturing even a very small amount of halogens contained in various resins, and can exhibit an excellent effect of preventing deterioration of the resins. In addition, the hydrotalcite-based compound particles of the present invention can be used in the form of particles or a molded product to exhibit a function of capturing anionic organic or inorganic compounds from a solution to a maximum extent without being dissolved, by themselves, in the solution.
Conventionally, in order to attain a good thermal stability of halogen-containing resins, in particular, when processed under heating, lead compounds have been frequently added thereto. However, in recent years, adverse influence of the lead compounds on environments and human bodies has been noticed, so that tin compounds, clay minerals such as hydrotalcite-based compounds, etc., which have a less burden on environments and human bodies, have been used in place of the lead compounds.
In general, the hydrotalcite-based compounds have a structure represented by the following chemical formula:[M2+1-xM3+x(OH)2]x+[An−x/n.yH2O]x−wherein M2+ represents at least one divalent metal ion selected from the group consisting of Mg2+, Zn2+, Ca2+, Fe2+, Co2+, Ni2+ and Cu2+, or Li+; M3+ represents at least one trivalent metal ion selected from the group consisting of Al3+, Fe3+, Mn3+ and Cr3+; An− represents a n-valent anion such as OH−, Cl−, CO32−, SO42− and inorganic and/or organic anions; x is a number of 0.2 to 0.56; and y is a number of usually 0.5, and may be a number of more than 0.5 when absorbing water therein, or 0.4 or 0.2 when subjected to dehydration treatment. When the hydrotalcite-based compounds are treated such that x is as close to 0 as possible, the structure of the hydrotalcite-based compounds is broken, so that the compounds are transformed into oxides or composite oxides. Therefore, the amount of crystal water contained in the hydrotalcite-based compounds is generally controlled to a level according to applications thereof.
The hydrotalcite-based compounds have a laminated crystal structure including a two-dimensional basic layer in which positively-charged octahedral brucite units are arranged in rows, and a negatively-charged intermediate layer. The hydrotalcite-based compounds used in the present invention preferably have such a structure represented by the above chemical formula in which M2+ is Ni2+, Cu2+, Fe2+, Mg2+, Ca2+, Zn2+ or Li+; M3+ is Al3+ or Fe3+; x is a number of 0.2 to 0.56; and An− is not particularly limited.
In the case where the hydrotalcite-based compound particles are used as a stabilizer for resins, in order to enhance a dispersibility of the particles in the resins, or prevent the hydrotalcite-based compounds themselves from being deteriorated due to halogens generated upon processing halogen-containing resins under heating, the surface of the respective hydrotalcite-based compound particles is usually coated with an organic compound.
For the purpose of protecting the hydrotalcite-based compound particles themselves, in particular, against halogens, the surface treatment is designed such that a whole surface of the respective particles is coated thick with the organic compound. However, the hydrotalcite-based compound particles whose surface is coated thick with the organic compound tend to be deteriorated in functions thereof, thereby failing to fully exhibit excellent effects on a thermal stability of stabilizers or resin compositions.
Also, the hydrotalcite-based compound particles have been used for removing halogen compounds, halogen ions or molecules and anionic organic or inorganic compounds from waste water.
As the method for removing a very small amount of iodine or anionic organic compounds contained in waste water, there may be exemplified a method of contacting the hydrotalcite-based compound in the form of particles or a molded product with waste water to remove substantially a whole amount of iodine or anionic organic compounds from the waste water by controlling contact area as well as treating temperature and time as well as amount of waste water passed therethrough. Further, there may also be exemplified a method in which the hydrotalcite-based compound is used in combination with activated carbon such that the adsorption in a region where a larger amount of iodine or anionic organic compounds are present in the waste water, is first conducted using the activated carbon, and then the adsorption in a region where only a very small amount of iodine or anionic organic compounds are present in the waste water, is conducted using the hydrotalcite-based compound.
However, the hydrotalcite-based compounds used for capturing or adsorbing halogens tend to be basically made of a Mg—Al-based material, a Ca—Al-based material or a mixed phase thereof. Therefore, when contacted with the waste water, the hydrotalcite-based compounds tend to suffer from not only elution of Mg or Ca as an alkali earth metal element, but also severe elution of Al when the waste water is highly alkaline or strongly acidic. For this reason, it is required to protect the surface of the respective hydrotalcite-based compound particles by coating the surface with an organic compound. However, in the conventional surface treatments, organic compounds used therein tend to be insufficient in kinds and treating amount to protect the surface thereof. As a result, when the surface-treated hydrotalcite-based compound particles are used for capturing or adsorbing halogens, the waste water after being subjected to capturing or adsorption of halogens using the surface-treated hydrotalcite-based compound particles, must be controlled in pH value thereof and then subjected to precipitation and filtration treatments to remove eluted elements such as Mg, Ca and Al from the waste water. This inevitably leads to necessity of additional equipments.
On the other hand, upon production of polyolefin resins or upon impart of a good flame retardancy to polyolefin resins or polyamide resins by adding a halogen-containing flame retardant or a halogen-containing flame retarding assistant thereto, these resins contain a very small amount of halogens, so that there tend to arise various problems such as deterioration of the resins when processed under heating. In order to prevent the deterioration of resins, as a halogen scavenger, there may be usually used the hydrotalcite-based compound particles.
In this case, in order to enhance a dispersibility of the hydrotalcite-based compound particles in the resins, or prevent the hydrotalcite-based compound particles themselves from being deteriorated upon processing the halogen-containing resins under heating, it has been required to treat the surface of the respective hydrotalcite-based compound particles with an organic compound.
In the surface treatment, in particular, in order to prevent deterioration of the hydrotalcite-based compound particles due to halogens generated, it has been strongly demanded that a whole surface of the respective hydrotalcite-based compound particles is coated thick with the organic compound. However, the hydrotalcite-based compound particles whose surface is wholly coated thick with the organic compound tend to come into a poor contact with the halogens and, therefore, tend to be deteriorated in function as a halogen catcher (scavenger).
To solve the above conventional problems, various surface-treating agents have been proposed in Japanese Patent Application Laid-open (KOKAI) Nos. 2002-212355, 2003-147227, 2002-293535, 2003-040614, 06-345963(1994), 07-062162(1995), 05-214177(1993), 2001-019428, 2000-024658, 2002-121461 and 11-349850 (1999), and Japanese Patent Application Publication (TOKUHYO) 2002-506910.
However, in the above-described documents, there are not described optimum combination of kinds and treating amounts of these surface-treating agents in view of attaining a good thermal stability of the halogen-containing resins or preventing initial coloration thereof.
Also, in the above-described documents, there are not described such hydrotalcite-based compound particles used as surface-treating agents which are optimized in the combination of kinds and treating amounts in order to capture a very small amount of halogens contained in polyolefin resins upon production thereof, or to prevent deterioration of polyolefin resins or polyamide resins due to a halogen-based flame retardant added thereto upon processing these resins.
Further, in the above-described documents, there are not described optimum combination of kinds and treating amounts of surface-treating agents composed of the hydrotalcite-based compound particles for the purposes of adsorbing anions contained in a solution such as waste water or minimizing dissolution of the hydrotalcite-based compound particles therein.
As a result of the present inventors' earnest study for solving the above conventional problems, it has been found that hydrotalcite-based compound particles which are surface-treated with an organic compound, and have a limited specific surface area as well as a specific conceptual value x corresponding to volumes of micropores and ultramicropores thereof and a specific conceptual value y corresponding to volumes of macropores and micropores thereof, can exhibit excellent effects on a thermal stability of resins and prevention of initial coloration thereof when added to the resins. The present invention has been attained on the basis of the above finding.